This disclosure generally relates to tracking systems that employ magnetic fields to determine the position and orientation of an object, such as systems used for tracking instruments and devices during surgical interventions and other medical procedures. More particularly, this disclosure relates to a system and method that utilizes at least one scalar-magnetometer for tracking.
Tracking systems have been used in various industries and applications to provide positional information relating to various objects and devices. For example, electromagnetic tracking is useful in aviation applications, motion sensing applications, medical applications, and the like. In medical applications, tracking systems are employed to provide information to an operator (e.g., a clinician) that assist in locating a medical instrument or device that is not in the line of sight of the clinician (e.g., disposed internal to a patient). The information generally includes an image having a base image displayed on a monitor, and a visual indication of the instrument's position. For instance, the image may include a visualization of the patient's anatomy with an overlay (e.g., icon) that represents the location of the instrument relative to the patient. Typically, the displayed image is continuously updated to reflect the current position of the device. The base image of the patient's anatomy may be generated prior to, or during the medical procedure. For example, any suitable medical imaging technique, such as X-ray, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and ultrasound, may be utilized to generate the base image. Accordingly, the combination of the base image and the representation of the tracked instrument provide positioning information that enables a medical practitioner to manipulate the instrument to a desired location and to associate gathered information to a precise location.
To track a device, tracking systems utilize a variety of methods, including magnetic field generation and detection. In a system utilizing magnetic field generation and detection, at least one magnetic field is provided from a magnetic field source (e.g., transmitter), and the magnetic field is sensed by one or more sensors (e.g., receivers). In some systems, the transmitter includes a permanent magnetic, an electromagnet, or a combination thereof. Further, the receiver generally includes a sensing device, such as a coil of conductive material that is responsive to a magnetic field. For example, when a receiver is exposed to a magnetic field, a current and voltage indicative of the strength of the magnetic field is driven across the coil. Thus, based on the sensed current and voltage, processing can determine the position of the transmitter and receiver relative to one another. For example, processing may enable a determination of the magnetic fields between each of the transmitters and the receivers, and may employ the ratios of the magnetic fields to resolve the positions of the transmitter and the receiver relative to one another.
Further, the tracking system may employ multiple transmitters and/or receivers that enable processing to precisely resolve position and orientation of the transmitters and receivers (e.g., the X, Y and Z coordinates, as well as the roll, pitch and yaw angles). In other words, multiple magnetic fields and receivers enable tracking to resolve several degrees of freedom. For example, the transmitter may be employed to provide multiple magnetic fields, and/or the system may include multiple receivers. Accordingly, the plurality measurements sensed between the transmitters and receivers can be employed to triangulate the position and/or the orientation of the transmitters and the receivers relative to one another.
Several factors may contribute to the accuracy of tracking applications. For example, field distorters (e.g., conductive objects) may induce eddy currents that distort the magnetic field and, thus reduce the overall accuracy of the tracking systems. One solution to this concern includes lowering the operating frequency (e.g., the frequency of the generated magnetic field) to reduce the effects of eddy currents. For example, the magnetic field frequency may be reduced from 14 kilohertz (kHz) to 14 hertz (Hz) to reduce the effects of field distorters. However, the sensitivity of a receiver coil is approximately proportional to the sensed frequency and the accuracy of the system may be reduced when the system operates at lower frequencies.
Accordingly, there is a desire to provide a tracking system wherein the receivers have increased sensitivities at lower frequencies.